From: peter@hurleysoftware•com (Peter Hurley)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 3/4] tty: omap-serial: use threaded interrupt handler
Date: Wed, 17 Sep 2014 08:01:08 -0400 [thread overview]
Message-ID: <54197804.3020302@hurleysoftware.com> (raw)
In-Reply-To: <20140916085037.GI28458@ci00147.xsens-tech.local>
On 09/16/2014 04:50 AM, Frans Klaver wrote:
> On Mon, Sep 15, 2014 at 01:31:56PM -0400, Peter Hurley wrote:
>> On 09/15/2014 11:39 AM, Peter Hurley wrote:
>>> On 09/15/2014 10:00 AM, Frans Klaver wrote:
>>>> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
>>>> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
>>>> this to about 170 overflows in 10 minutes.
>>>
>>> Why is the threadirqs kernel boot option not sufficient?
>>> Or conversely, shouldn't this be selectable?
>>
>
> I wasn't aware of the threadirqs boot option. I also wouldn't know if
> this should be selectable. What would be a reason to favor the
> non-threaded irq over the threaded irq?
Not everyone cares enough about serial to dedicate kthreads to it :)
>> Also, do you see the same performance differential when you implement this
>> in the 8250 driver (that is, on top of Sebastian's omap->8250 conversion)?
>>
>
> I haven't gotten Sebastian's driver to work properly yet on the console.
> There was no reason for me yet to throw my omap changes on top of
> Sebastian's queue.
>
>>> PS - To overflow the 64 byte RX FIFO at those data rates means interrupt
>>> latency in excess of 250us?
>
> At 3686400 baud it should take about 174 us to fill a 64 byte buffer. I
> haven't done any measurements on the interrupt latency though. If you
> consider that we're sending about 1kB of data, 240 times a second, we're
> spending a lot of time reading data from the uart. I can imagine the
> system has other work to do as well.
System work should not keep irqs from being serviced. Even 174us is a long
time not to service an interrupt. Maybe console writes are keeping the isr
from running?
Regards,
Peter Hurley
next prev parent reply other threads:[~2014-09-17 12:01 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-15 14:00 [PATCH v3 0/4] omap-serial high-speed fixes/improvements Frans Klaver
2014-09-15 14:00 ` [PATCH 1/4] tty: omap-serial: pull out calculation from baud_is_mode16 Frans Klaver
2014-09-15 14:00 ` [PATCH 2/4] tty: omap-serial: prevent division by zero Frans Klaver
2014-09-15 14:00 ` [PATCH 3/4] tty: omap-serial: use threaded interrupt handler Frans Klaver
2014-09-15 15:39 ` Peter Hurley
2014-09-15 17:31 ` Peter Hurley
2014-09-16 8:50 ` Frans Klaver
2014-09-17 12:01 ` Peter Hurley [this message]
2014-09-17 12:13 ` Frans Klaver
2014-09-23 8:24 ` Frans Klaver
2014-09-23 17:17 ` Peter Hurley
2014-09-23 18:11 ` Frans Klaver
2014-09-23 18:38 ` Tony Lindgren
2014-09-23 20:02 ` Frans Klaver
2014-09-15 14:00 ` [PATCH 4/4] tty: omap-serial: support setting of hardware flow control in dts Frans Klaver
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